Is Zakat obligatory on a plot of land that was purchased with money withdrawn from the bank to avoid usurious interests?

Your father must repent from dealing with the usurious bank and dispose of the usurious interest by spending it on the welfare of Muslims or giving it to the poor and needy.

As for the plot of land, if it was purchased with the intention of trade, then zakat is due on it by appraising it every Hijri year and giving out one-quarter of one-tenth of its value. If it was purchased for purposes other than trade (such as building on it, renting it out, or without a specific intention), then there is no zakat on it, based on the Prophet's (peace and blessings be upon him) saying: "There is no sadaqah [zakat] due on a man's slave or his horse."